The invention concerns a fan blower or centrifugal throwing wheel for ejection of blasting materials onto workpieces to be blasted.
The blasting technique has long been known. It is used for deburring of molded parts, for roughing up surfaces, compacting, rust removal, removal of scales, removal of lacquer and coating from surfaces, for separation of different materials, peeling of food items, and for mincing. Many blasting processes are possible only with additional heat or cold, e.g., flame blasting, cold deburring of elastomers, removal of lacquer from festooning in varnishing machines, from transport devices and gridirons, for cold mincing and cold peeling of food items. In all applications, a large blasting surface with uniform kinetic blasting energy and density is required.
However, with the currently used throwing wheels, this is not achieved to an optimum degree. These throwing wheels have a relatively simple design and generally consist of two parallel discs with ejection scoops or vanes arranged between them. The vanes are radially arranged fins with smooth or at most slightly profiled ejection or throwing surfaces. The inner surfaces of the two discs or plates are designed to form a V-shaped slot and thus, the distance between them increases outwards from the center. This determines an angle .alpha. between the two discs.
Preferably, the blasting material is ejected in the rotation plane of the wheel, while density and energy of the ejected material decrease strongly to the left and to the right of the rotation plane. The blasting pattern of the entire surface on which the blasting material has impacted is thus far from uniform. While there is a very intensive blasting effect and impact frequency in the center of the surface, this decreases significantly towards the edges. This is a great disadvantage in respect to the processing of sensitive workpieces, since on one hand, there will be a large quantity of rejects, i.e., workpieces which have been blasted too strongly or not uniformly enough, and, on the other hand, many workpieces must be reworked, namely if the blasting effect has been insufficient. Furthermore, this is a disadvantage in all blasting treatments executed with additional heat or cold, since there is low utilization of the heat or cold. This is due to the fact that if additional cold is required, more cooling of the workpieces is required than if the blasting effect is uniform. For this reason, devices are used, in which the blasted workpieces are being moved and turned around during the blasting process. Such devices are known, e.g., from the German Patent Document No. 25 16 721 and the German Disclosure Document No. 26 50 202. These known devices ascertain that the workpieces are turned around and that their surfaces are thus uniformly exposed to the blasting material. However, it cannot be achieved that all workpieces are uniformly moved through zones of high blasting density and blasting energy and zones of low blasting density and blasting energy. Disregarding this, such movement of the workpieces is impossible in respect to many workpieces, particularly if they are large.